Intravenous injection of autologous amniotic fluid induces transient thrombocytopenia in a gravid rabbit model of amniotic fluid embolism

Abstract

Amniotic fluid embolism (AFE) is a rare but catastrophic complication of pregnancy characterized by severe hypotension, cardiovascular collapse, and massive consumptive coagulopathy. Several animal models of this syndrome have been proposed, but most have yielded inconclusive results. The objective of this study was to develop a suitable animal model of AFE. Twelve rabbits in late gestation (25 days) were used. Amniotic fluid was collected from the fetal amniotic sacs after laparotomy, and autologous fluid was injected into 6 rabbits via the left auricular vein. Six other rabbits received saline (control group). Blood pressure, platelet counts, and coagulation variables were measured at baseline and at various intervals for 60 minutes after injection. The in vitro effect of amniotic fluid on coagulation was assessed by thrombelastographic (TEG) analysis. Injection of amniotic fluid did not reproduce clinical signs of AFE and had no effect on activated partial thromboplastin time (aPTT), prothrombin time (PT), or Factor VIII activity. However, significant thrombocytopenia was observed 5 minutes after administration of amniotic fluid and resolved by 60 minutes. In vitro addition of amniotic fluid to blood resulted in accelerated clotting on TEG tracings. The syndrome of AFE was not reproduced in this rabbit model. However, injection of autologous amniotic fluid induced a transient and severe thrombocytopenia. Moreover, TEG analysis indicated that amniotic fluid could initiate the coagulation cascade. Other factors such as the presence of meconium in amniotic fluid may be needed to provoke more severe clinical signs.